For many patients suffering from retinal degenerative diseases such as advanced or age-related macular degeneration (AMD) and retinitis pigmentosa (RP) there has been little hope for maintaining vision. Every year, 700,000 new cases of AMD in the U.S. are diagnosed and 10% of those patients will become legally blind. There are presently no cures for these debilitating diseases, and, at best, current treatments only slow the disease progression. The overall social and economic impact of AMD and RP is immense and the importance of treating blindness is profound as this is a problem of significant scope and breadth. There is an unmet need to treat this ailment by developing a visual prosthetic with a large number (e.g., thousands) of stimulation channels to realistically restore sight using infrared light to stimulate the retinal nerves. Advanced macular degeneration and retinitis pigmentosa are both diseases that degrade vision in patients and eventually will lead to blindness.
Researchers have artificially stimulated various parts of the human nervous system for many years as a way to restore lost or damaged neural function of various systems in the human body. Neuroprosthetic devices circumvent non-functioning physiological structures (hair cells in the ear, rods and cones in the eye) which would normally transduce an external stimulus (sound, light) into an action potential. Presently, there are numerous efforts underway to develop neuroprostheses to restore sight at various interventional anatomical locations: in the subretina, the epiretina, the optic nerve and in the visual cortex. These devices apply an electric current pulse to stimulate the neurons of the visual system which is inherently hindered by a lack of spatial selectivity. Electrical current spread leads to imprecise nerve stimulation and limits the ability of the neuroprosthesis to restore function. The limitation of spatial selectivity is based on fundamental physical principles of electrical stimulation. To date, after 20 years of development, electrical implants are just now hoping to make the jump to 64-channel systems from 16-channel systems. This is far less than the thousands of channels estimated to be needed for a good vision prosthetic. The technology is further limited by the fact that physical contact is required with tissue, which can lead to damage over time. Implantation of a complex powered device in very close proximity to sensitive neural tissue forms a significant drawback to this approach, making it impossible to update the technology without further risky surgeries.
There have been rudimentary attempts to stimulate the retinal nerves with electrical signals, which are being conducted by various groups globally. For example, the Argus™ II implantable device, by Second Sight Medical Products, Inc., 12744 San Fernando Road—Building 3, Sylmar, Calif. 91342, USA, which is intended to treat profoundly blind people suffering from degenerative diseases such as RP. The Second Sight Medical Products, Inc. Argus™ II system works by converting video images captured from a miniature camera, housed in the patient's glasses, into a series of small electrical pulses that are transmitted wirelessly to an epiretinal prosthesis array of electrodes implanted inside the eye on the retina. These pulses then stimulate the retina's remaining cells resulting in the corresponding perception of patterns of light in the brain. Patients supposedly learn to interpret these visual patterns thereby gaining some functional vision.
U.S. Pat. No. 7,079,900 issued Jul. 18, 2006, to Greenburg et al., titled “Electrode Array for Neural Stimulation,” is incorporated herein by reference. Greenburg et al. describe a retinal color prosthesis to restore color vision by electrically stimulating undamaged retinal cells, which remain in patients with lost or degraded visual function. There are three main parts: one is external to the eye, the second part is internal to the eye, and the third part communicates between those two parts. The external part has color imaging means (CCD or CMOS video camera), an eye-tracker, a head-motion tracker, a data processor, a patient's controller, a physician's local controller, a physician's remote controller, and a telemetry means. The color data is processed in the video data processing unit and encoded by time sequences of pulses separated by varying amounts of time, and also with the pulse duration being varied in time. The basis for the color encoding is the individual color code reference. Direct color stimulation is another operational basis for providing color perception. The electrodes stimulate the target cells so as to create a color image for the patient, corresponding to the original image as seen by the video camera. The physician's test unit can be used to set up or evaluate and test the implant during or soon after implantation.
U.S. Pat. No. 7,914,842 issued Mar. 29, 2011, to Greenberg et al., titled “Method of Manufacturing a Flexible Circuit Electrode Array,” is incorporated herein by reference. Greenberg et al. describe polymer materials and electrode array bodies for neural stimulation, especially for retinal stimulation to create vision. The method lays down a polymer layer, applies a metal layer to the polymer and pattern to create electrodes and leads, and applies a second polymer layer over the metal layer and pattern to leave openings for electrodes. The array and its supply cable are a single body.
Electrical stimulation represents a major challenge in developing implantable devices with long-term system performance while reducing their overall size. The Boston Retinal Implant Project has identified long-term biocompatibility as one of the most significant challenges to be met in order to develop a successful retinal prosthesis. For example, U.S. Pat. No. 6,324,429 issued Nov. 27, 2001, to Shire et al., titled “Chronically Implantable Retinal Prosthesis,” is incorporated herein by reference. Shire et al. describe a chronically implantable retinal prosthesis for the blind which will restore some useful vision to patients over at least several degrees of their former field of view. These thin, strong, and flexible epiretinal devices are constructed of or encapsulated in known biocompatible materials which will have a long working life in the eye's saline environment. The function of the implants is to electrically stimulate the ganglion cell layer at the surface of the retina using controlled current sources. Due to the exceptionally low mass of the implant and its flexible, nearly planar form, patient discomfort and fluid drag caused by the implant minimized. These physical attributes also substantially reduce the potential of harm to the most delicate structure of the eye, the retina, and therefore enhance the long term safety and biocompatibility of the device. Since no micro-cables are required to be attached to the device, and its overall form and edges are rounded, the device is not expected to stress the retina during chronic implantation. A provision is also made for nutrients to reach the retinal cells underneath the device to assure their long-term health.
U.S. Pat. No. 7,908,010 issued Mar. 15, 2011, to Greenberg et al., titled “Retinal Prosthesis with Side Mounted Inductive Coil,” is incorporated herein by reference. Greenberg et al. describe a retinal prosthesis with an inductive coil mounted to the side of the eye by means of a strap around the eye. This allows for close coupling to an external coil and movement of the entire implanted portion with movement of the eyeball.
Electrical stimulation, as described in the above devices and patents, is limited since the spread of electricity does not allow separate or independent stimulation of individual retinal nerve cells or even small-enough groups of nerve cells for sharp or clear vision. This electrical-stimulation technology is severely limited, as electricity spreads in human tissue and thus will severely limit the number of stimulation sites. Electrical stimulation thus greatly limits the number of sites that could be separately stimulated. Additionally, the electrical-stimulation approach will require implantation of a powered (e.g., an electrically powered) device, which has significant, difficult issues associated with obtaining power into the eye and using the power by devices in the eye.
Other work is being done in the area of optogenetics wherein a virus is used to genetically sensitize nerve cells to certain wavelengths of light, e.g., PCT publication WO 2010/011404 A2 titled “Vectors for Delivery of Light-Sensitive Proteins and Methods of Use,” which is incorporated herein by reference. This area may have some potential, however it will require significant development work, it involves injecting a virus into nerve tissue (which may have significant side effects and FDA-approval issues), and the virus is only partially taken up by nerve cells.
Materials that are compatible with the eye are described in U.S. Pat. No. 6,254,637 to Jin Hak Lee et al., titled “Artificial Cornea and Implantation Thereof”; U.S. Pat. No. 6,391,055 to Yoshito Ikada et al., titled “Artificial Cornea”; U.S. Pat. No. 6,976,997 to Noolandi et al., titled “Artificial Cornea”; U.S. Pat. No. 7,857,849 to David Myung et al., titled “Artificial corneal implant”; and U.S. Pat. No. 7,909,867 to David Myung et al., titled “Interpenetrating Polymer Network Hydrogel Corneal Prosthesis”; each of which is incorporated herein by reference in its entirety.
Numerous digital light projection micro-electro-mechanical-system (MEMS) devices exist. For example, U.S. Pat. No. 4,566,935 issued to Hornbeck on Jan. 28, 1986, titled “Spatial Light Modulator and Method” and is incorporated herein by reference in its entirety. Hornbeck described methods of fabrication of spatial light modulators with deflectable beams by plasma etching after dicing of a substrate into chips, each of the chips an SLM. Various architectures available with such plasma etching process were disclosed and include metal cloverleafs for substrate addressing, metal flaps formed in a reflecting layer over a photoresist spacer layer, and torsion hinged flaps in a reflecting layer.
As another MEMS display example, U.S. Pat. No. 7,776,631 issued to Miles on Aug. 17, 2010, titled “MEMS Device and Method of Forming a MEMS Device,” and is incorporated herein by reference in its entirety. Miles described light in the visible spectrum being modulated using an array of modulation elements, and control circuitry connected to the array for controlling each of the modulation elements independently, each of the modulation elements having a surface which is caused to exhibit a predetermined impedance characteristic to particular frequencies of light.
U.S. Pat. No. 7,177,081 issued to Tomita et al. on Feb. 13, 2007, titled “High Contrast Grating Light Valve Type Device,” and is incorporated herein by reference in its entirety. Tomita et al. describe a grating light valve with a plurality of spaced reflective ribbons that are spatially arranged over a substrate with reflective surfaces. The grating light valve is configured to optimize the conditions for constructive and destructive interference with an incident light source having a wavelength λ. The grating light valve preferably has a set of movable active ribbons alternating between the set of stationary bias ribbons. In operation, active ribbons are moved by a multiple of λ/4 to switch between the conditions for constructive and destructive interference.
U.S. Pat. No. 4,720,189 issued Jan. 19, 1988 to Heynen et al., titled “Eye-Position Sensor,” is incorporated herein by reference in its entirety. Heynen et al. describe an eye-position sensor for use in an eye-activated optical transducer in which a spatial filter is used to modify light reflected from the eye to form a substantially rectangular pattern on a quadrantal array of contiguous sensors. This arrangement provides a substantially linear change in the output signal from the sensors in response to an equivalent movement of the eye.
U.S. Pat. No. 6,055,110 issued Apr. 25, 2000, to Kintz et al., titled “Compact Display System Controlled by Eye Position Sensor System,” is incorporated herein by reference in its entirety. Kintz et al. describe a virtual image display system is provided which is made thinner through the use of an immersed beam splitter, and in one embodiment, total internal reflection. The display system includes an imaging surface on which a source object is formed, a first optical element having a reflective function and a magnification function, a second optical element having a magnification function and an immersed beam splitting element positioned between the first and second optical elements, the immersed beam splitting element including a beam splitter surrounded by an optically transparent material having a refractive index greater than air. An illumination source projects the source object formed at the imaging surface through the optically transparent material to the beam splitter. The beam splitter reflects the projected source object to the first optical element. The first optical element magnifies the projected source object and reflects a magnified virtual image of the projected source object to the beam splitter. The magnified virtual image traverses the beam splitter to the second optical element which magnifies the magnified virtual image to produce a compound magnified virtual image of the source object.
There remains a need in the art for an improved prosthesis and method for stimulating vision nerves to obtain a vision sensation that is more useful for the patient.